1. Field of the Invention
The present invention relates to a sheet conveying apparatus comprising a plurality of drive motors for conveying sheets. The sheet conveying apparatus is suitable for use in laser beam printers, copying machines, etc.
2. Description of the Related Art
Image forming apparatus, such as a laser beam printer, which performs printing by transferring a toner image formed on the drum to a predetermined area of a recording sheet, generally comprises two motors provided respectively for driving the printing section for continuously forming images and driving the sheet feeding section for supplying sheets to the printing section. These separate motors facilitate efficient print position control including timing control of electrostatic initialization of the printing section, sheet pick-up from the sheet stacker in the sheet feeding section, and re-feeding by the sheet feeding section in accordance with the image forming timing of the printing section. Such print position control can be performed simply by controlling the operations of the individual motors.
However, because the separate drive systems for the sheet feeding section and the printing section have different moments of inertia and cause different drive losses, they require different lengths of time to stop in response to a motor stop signal. In many image forming apparatuses, the printing section, situated downstream of the sheet feeding section, has a larger moment of inertia and therefore requires a longer time to stop than the sheet feeding section. If an emergency stop motor signal is output in such an apparatus due to, for example, sheet jamming, while a sheet is being transferred from the sheet feeding section to the printing section, the sheet is held tense between the two sections. That is because the printing section forcibly pulls the sheet from the sheet feeding section. In such cases, the drive systems, the drum and the like receive excessively large loads, thereby reducing the durability and service life of the apparatus.